This invention relates to a catalytic process for producing methanol directly from synthesis gas. more particularly, the invention concerns reacting synthesis gas, i.e., mixtures of hydrogen and carbon monoxide, in the presence of a stable ruthenium carbonyl complex catalyst to directly form methanol.
Methanol is an increasingly important feedstock for the production of carbon-based chemicals. Existing or proposed commercial processes using methanol include dehydrogenation to form formaldehyde, carbonylation to form acetic acid, homologation to form ethanol and reactions over zeolitic materials to form gasoline grade fractions. Owing to the reduced availability of petroleum, the cost of producing chemicals from petroleum has been steadily increasing and the anticipated increase in commercial methanol manufacture has underscored the need for a different, low cost source which can be converted into chemicals.
Synthesis gas, which is derived by the combustion of any carbonaceous material including coal, or any organic material, such as hydrocarbons, carbohydrates and the like has for a long time been considered a desirable starting material for the manufacture of a variety of chemicals. Hydrocarbons have been made by the Fischer-Tropsch catalytic reaction. Methanol is commercially manufactured by a heterogeneous catalytic reaction from synthesis gas. Aldehydes and alcohols are made from the reaction of olefins and synthesis gas.
One of the deficiencies of known processes for making chemical products from synthesis gas involves the use of heterogeneous catalysts or, when using a homogeneous catalytic reaction, employing a rhodium carbonyl complex catalyst which is extemely expensive. Rhodium is employed in auromotive catalytic converters which comprise the combustion devices for reducing automotive pollutant emissions. The high cost of rhodium is created by its limited availability and the tremendous demand for it. Thus, a commercial process which uses rhodium as a catalyst is affected by the high capital expense to purchase the metal and the strict controls needed to limit catalyst losses in order to keep the economics of the process competitive.* Ruthenium, on the other hand, is a precious metal which has no significant commercial application. Its present cost is approximately 1/20th, and less, that of rhodium even through its concentration in the ore from which both are obtained is about the same. FNT * See Cornils, et al., Hydrocarbon Processing, June, 1975, pp. 83 to 91.
Ruthenium has been explored as a catalyst by many. It has been considered as a hyrogenation catalyst, as an alcohol homologation catalyst, as a catalyst to produce a wide range of monohydric alcohols (non-specific as to any of them) exclusive or methanol, as an alcohol homologation catalyst such as for the conversion of methanol to ethanol,** and as a high pressure catalyst to selectively produce methanol and methyl formate. FNT ** See, for example U.S. Pat. Nos. 4,133,966 and 3,285,948; and Japanese patent application (Kokai) No. 52-73804/77 (June 21, 1977) [application No. 50-149391/75 (application date, Dec. 15, 1975)] to Mitsubishi Gas Chemical Industry Company.
For example, in a recent report (Journal of the American Chemical Society, vol. 101, pp. 7419-21 (1979)) J. S. Bradley of Exxon Corporation produced methanol and methyl formate at a selectivity greater than 99% without hydrocarbon products detected, by the reaction of synthesis gas (H.sub.2 :CO.dbd.2:1) under pressures on the order of 1,300 atmospheres and at temperatures around 270.degree. C. using a Ru catalyst, which under the conditions of the reaction was present as Ru(CO).sub.5. Bradley reported that no homologation products were found.
In Willismson, et al., U.S. Pat. No. 4,170,605, patented Oct. 9, 1979, the patentees report in Examples I and II the reaction in 1-propanol of synthesis gas (CO:H.sub.2 .dbd.1:1) at 25,000 psig and at 230.degree. C. using ruthenium tris(acetylacetonate) and 2-hydroxypyridine for a period of 2 and 3 hours, respectively. In Example I, Williamson, et al. report the production of 4 grams of product* containing (mole percent basis): ethylene glycol, 57; and methanol, 25. In Example II, 7 grams of product* are reported containing 66 and 16 mole percent of ethylene glycol and methanol, respectively. FNT * Included in the 4 and 7 grams of product are trace amounts of water and methylformate, as well as 16 mole % (Example I) and 15 mole % (Example II) of propylformate. The latter compound would appear to be derived form 1-propanol initially present in the reaction mixture, rather than a synthesis gas-derived product.
Further, in copending application Ser. No. 91,242, filed Nov. 15, 1979, now abandoned in favor of continuing application Ser. No. 319,887, filed Nov. 10, 1981; Ser. No. 358,703, filed Mar. 16, 1982 and Ser. No. 359,778, filed Mar. 19, 1982, there is described a process for selectively producing methanol, ethanol, and ethylene glycol by reacting carbon monoxide and hydrogen in a homogeneous liquid phase mixture containing a ruthenium carbonyl complex. The reaction is effected at a temperature between about 50.degree. C. to about 400.degree. C. and a pressure of between about 500 psia (35.15 kg/cm.sup.2) and about 15,000 psia (1,054.6 kg/cm.sup.2) for a period of time sufficient to produce such products; and in U.S. Pat. No. 4,323,513, there is described an improved process for producing methyl and ethylene glycol esters as described in U.S. Ser. No. 91.242 in which the improvement comprises maintaining the combined concentration of methyl ester, ethylene glycol ester and water in the reaction medium at less than about 30 vol. %.
Thus, while previously known processes using homogeneous ruthenium catalysts will produce methanol with high selectivity, generally very high pressures are required or other products are also produced and it would be desirable to produce only methanol or derivatives thereof at high process efficiency and low or moderate pressures.